Lisa, I'm so sorry to hear this. The only time I experienced this was when I only had 3 cats, Storm, Pepper, and Sunny. I took them all to my vet at the same time for some routine things and a few days later Storm became ill. Then both Pepper and Sunny became ill. I didn't have to take Sunny and Pepper in for an exam since they had the same thing. The problem was that Pepper weighed a lot more than either Storm or Sunny and he became sicker and sicker so please be sure that if you don't have to take them in for an exam that you get the right dosage of meds for them. Hopefully it won't spread to all of your cats. Lots of prayers and positive thoughts are being sent your way. Please take care. (((HUGS)))